Enantioselective permeation of various racemates through an optically active poly{1-[dimethyl(10-pinanyl)silyl]-1-propyne} membrane

Optical resolution of various racemates such as (+/-)-tryptophan and (+/-)-1,3-butanediol was achieved by permeation through a self-supporting membrane of (+)-poly{1-[dimethyl(10-pinanyl)silyl]-1-propyne} [(+)-poly(DPSP)] prepared by homopolymerization of (-)-1-[dimethyl(10-pinanyl)silyl]-1-propyne [(-)-DPSP]. Almost complete optical resolution (% ee of the permeate = 81-100% ee) was achieved at an initial period of concentration-driven permeation, and stable permeation with moderate permselectivity (% ee of the permeate = 12-54% ee) continued for more than 600 h. In addition, by permeation of vapor permeant such as evapomeation and pervaporation, higher permeation rates were attained maintaining high enantioselectivity. The sign of the enantiomer that predominantly permeated through a (+)-poly(DPSP) membrane was opposite to that through a (-)-poly(DPSP) membrane. In the permeation through a (+)-poly(DPSP) membrane of a solute or a solvent having a high affinity for (+)-poly(DPSP) and in the permeation through a membrane from the copolymer of (-)-DPSP with a small amount of 1-(trimethylsilyl)-1-propyne, their enantioselectivities were much lower. These findings suggest that the permeating route surrounding chiral pinanyl groups in a (+)-poly(DPSP) membrane that can enantioselectively separate various racemates was easily deformed by using a solute or solvent having a high affinity for (+)-poly(DPSP) or by removing a small amount of pinanyl groups.